The homeobox transcription factor MrHOX7 contributes to stress tolerance and virulence in the entomopathogenic fungus Metarhizium robertsii.

Entomopathogenic fungi, including Metarhizium species, represent promising environmentally friendly biopesticides. Understanding the molecular mechanisms governing their infection processes is vital for enhancing their effectiveness. Transcription factors (TFs) play critical roles in gene regulation, yet the functions of many TFs in M. robertsii remain unknown. Homeobox transcription factors, implicated in diverse cellular processes, have received limited attention in entomopathogenic fungi. Here, we identify and characterize, a homeobox TF, MrHOX7, in the model entomopathogenic fungus M. robertsii. Subcellular localization and transcriptional profiling revealed MrHOX7's nuclear localization and high expression during conidia and appressoria formation. Deletion of Mrhox7 (ΔMrhox7) enhanced conidial tolerance to heat and UV-B stress, accompanying with upregulated stress-related gene expression. Intriguingly, ΔMrhox7 exhibits inhibited virulence exclusively through topical inoculation. Further investigations unveiled reduced conidial adhesion and appressorium formation, with downregulation of the adhesion gene Mad1 and appressorium-related genes, as the underlying causes of the reduced fungal virulence. Our findings illuminate the role of MrHOX7 in stress tolerance and virulence, providing insights into the molecular basis of fungal biopesticides.